In ink-jet printing methods, droplets of ink are directly projected onto a printing medium from very fine nozzles and allowed to adhere to the printing medium to form characters or images thereon. The ink-jet printing methods have now been employed not only in printing applications for ordinary consumers, but also recently in commercial and industrial printing applications because of various advantages such as easiness of full coloration, low cost, capability of using a plain paper as the printing medium, non-contact with printed characters or images, etc. As a pigment for a yellow ink used in the ink-jet printing methods, C.I. Pigment Yellow 74 has been extensively used.
JP 2008-63524A (Patent Literature 1) discloses an ink composition containing C.I. Pigment Yellow 74 which is excellent in light resistance and free of ejection defects when used in ink-jet printing methods, in which a content of an anisidide compound having a specific structure in the ink composition is 1 to 20 ppm.
Also, JP 2014-177575A (Patent Literature 2) discloses a process for producing a pigment composition as a method of improving transparency, coloring properties and light resistance of a monoazo yellow pigment composition, which includes a first step of obtaining a crude monoazo pigment composition containing a monoazo pigment and a monoazo compound obtained by a specific reaction, the monoazo compound being contained in a specific amount on the basis of the monoazo pigment, and a second step of subjecting the thus obtained crude monoazo pigment composition to finishing treatment at 115° C. in an autoclave.